Recent improvements in automobile efficiency and fuel-consumption led to increase of temperature in the automobile engine compartment. As a result such rubber materials as acrylo-nitrile-butadiene copolymers, hydrogenated acrylo-nitrile-butadiene copolymers, or similar acrylo-nitrile rubbers; acrylic rubbers, copolymers of ethylene and acrylic acid ester, copolymers of acrylic acid ester, ethylene, and vinyl acetate, or similar acrylic rubbers; EPM, EPDM, or similar ethylene-propylene rubbers, etc., which are conventionally used for manufacturing parts exposed to high temperatures of the engine compartment appeared to be insufficient in their resistance to heat. On the other hand, silicone rubbers have normally insufficient resistance to fuel oil and are highly permeable to gases, and therefore their use is limited, especially in areas where they can be exposed to fuel oils or fuel-oil-vapors.
It was proposed to solve the above problem by forming a rubber laminate from silicone rubber and rubber other than silicone rubber. In particular, it was proposed to form a silicone laminate body by incorporating a fluororubber, which is characterized by excellent resistance to chemicals and fuel oils. However, since fluororubber has low surface energy and low reactivity, it is difficult to provide strong bonding between a fluororubber layer and a silicone-rubber layer. Therefore, several studies have been undertaken in order to solve the above problem.
For example, a method was proposed for simultaneous cross-linking and curing a non-cross-linked silicone rubber and a non-cross-linked fluororubber while maintaining both rubbers in mutual contact (see Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) 2000-193152). Furthermore, Kokai 2003-19772 discloses a rubber laminate obtained by simultaneously vulcanizing a layer of fluororubber, which is mixed with a silica-type filler and contains vinylidene-fluoride units, and a layer of silicone rubber, which contains a silica-type filler and a silane-coupling agent that contains amino groups. Kokai 2003-214565 discloses a rubber hose having an intermediate layer of a silicone rubber that contains an adhesive component and is placed between a fluororubber layer and a silicone-rubber layer. However, provision of the adhesive component in the silicone rubber impairs its heat-resistant properties and handling conditions and therefore limits application of the aforementioned laminates. Furthermore, exposure of the laminate to hot environment weakens bonding between the fluororubber layer and the silicone rubber.